Features I'd like to see implemented to sound system:
Speed of sound. Sound from distant explosions arrive in relation to distance.
Advanced equalization of sounds. The low frequencies travel longer distances and pass obstacles easier. Distant explosions need to be "boomier" i.e. missing high frequencies as well as sounds passing great obstacles.
Effects of obstacles to sound. i.e. entering a valley or flying behind a mountain should block sound to some extent.
Smooth onset and decay of sounds. The sounds from aircraft coming to range need to start smoothly as tehy enter and stop smoothly as they exit the audible range.
Weapon audible RoF needs to match their actual RoF.
More variation to hit sounds.
Sounds from damage. I.e. turbulence sound from missing gear, holes in fuselage and cockpit.
Chance to adjust a realistic level of cockpit sounds. I.e. you do not hear much else in a real aircraft and the head gear changes the actual pitch of sounds you manage to hear.
More?
-C+